1. Field of the Invention
This invention relates to a toner and a process cartridge which are used in image-forming processes such as electrophotography, electrostatic printing and toner jet printing. More particularly, it relates to a toner for developing electrostatic latent images, and an image-forming method and a process cartridge which make use of the toner.
2. Related Background Art
In recent years, in electrophotographic image-forming apparatus, a process cartridge system has widely been employed in which an electrophotographic photosensitive member and other processing means to be set to act on the photosensitive member are integrally joined to set up a cartridge so as to be detachably mountable to the main body of an electrophotographic image-forming apparatus. In the electrophotographic image-forming apparatus of such a cartridge system, users themselves can replace the cartridge, and hence some apparatus are provided with a means for detecting the quantity of toner remaining in a developing unit and, when the toner is running short, indicating its quantity to warn and urge users to replace the cartridge before any lowering of image density occurs.
Various methods are proposed on such detection of cartridge""s service life, and a method is proposed in which a non-volatile storage means such as EEPROM (electrically erasable programmable read-only memory) is utilized to integrate the usage (extent of use) of a cartridge and store it in memory. For example, Japanese Patent Application Laid-open No. 61-185761 discloses an electrophotographic image-forming apparatus having a means by which, where a photosensitive drum in a process cartridge is exposed to light of a laser or a light-emitting diode, the information of the exposure time is added and stored in memory so that the information corresponding to the residual (residual quantity) of toner is added and stored in memory.
On such a cartridge, since there are many opportunities for the cartridge to be detached from and mounted to the main body of the apparatus, it is also proposed to incorporate a storage means in the cartridge itself so that the accuracy of detection may be improved when a plurality of cartridges are used for one apparatus main body. For example, as disclosed in Japanese Patent Application Laid-open No. 63-212956, an electrophotographic image-forming apparatus is proposed in which a cartridge is provided therein with a memory and the apparatus main body is provided with a means for reading and writing stored information and a means for operating information relating to the cartridge""s service life in accordance with what has been read from the memory and with electrophotographic action to write the information in the memory.
As another method of detecting the consumption of toner, a method is also proposed in which the residual of toner in a cartridge is directly detected. For example, Japanese Patent Application Laid-open No. 62-62352 discloses a method in which a detecting antenna is provided in the vicinity of a developing sleeve which is a toner-carrying member, and electric current induced in the antenna is measured when AC voltage is applied to the developing sleeve, where any change of the electric current in accordance with the quantity of toner present between the sleeve and the antenna is utilized to detect the residual of toner.
Japanese Patent Application Laid-open No. 5-100571 also discloses a toner detector having a toner-detecting electrode member in which, in place of two electrode rods, two parallel electrodes, disposed on the same plane in parallel keeping a stated distance between them, are combined in plurality in a hill-and-dale fashion; the toner-detecting electrode member being disposed at the bottom surface of a toner container. This detector detects any change in electrostatic capacity between the parallel electrodes provided in a planar state, to detect the residual of toner.
However, all the above toner detectors detect whether or not the toner remains in the toner container, i.e., they can only detect that the toner is running short immediately before the toner held in the toner container is used up, and can not detect how much the toner remains in the toner container.
On the other hand, where the quantity of toner in the toner container can be detected, it is possible for users themselves to know the condition of use of toner in the toner container. This is very convenient for users because a new process cartridge can be prepared for replacement at an appropriate time.
Such a successive residual detection system is disclosed in, e.g., Japanese Patent Applications Laid-open No. 2000-147891, No. 2000-206774, No. 2000-250380, No. 2001-27841 and No. 2001-27842, which, however, has room for studies on the detection of residual in high precision.
The residual detection systems having been discussed above also have a problem that the quantity of a toner filled into a cartridge is measured and hence the detection may greatly be influenced by power characteristics of the toner. Especially where the toner is filled into the cartridge in a large volume, or the cartridge has such a shape that it tends to be densely packed with the toner, the toner may have a poor fluidity depending on service environmental conditions of printers, so that the quantity of toner can not accurately be detected or the detection system can not operate in some cases.
Accordingly, where such a system is employed, it is preferable to learn the powder characteristics of toner by using a method of evaluating toner""s fluidity as one of characteristics of powder. The fluidity of individual toners may be evaluated by any methods suited for the toners. It, however, is also true that there is a possibility of lacking in generality. Accordingly, the Carr""s fluidity index and Carr""s floodability index are available as indices by which the fluidity of powder can synthetically been evaluated by measuring some phenomena and characteristics relating to fluidity.
The fluidity index can literally be a standard for evaluating the difficulty of flow-out ascribable to the force for gravity on powder, and the floodability index is a standard for determining how the phenomenon of flushing tends to occur. Flushing is a phenomenon in which the powder having been kept stationary to have a low fluidity comes into a fluidized state like a liquid when vibrated to begin being fluidized.
It means that, the higher the value of this floodability index is, the higher fluidity and floodability the toner has as a powder.
As patents in which these values are specified, Japanese Patent Publication No. 59-21549 discloses a toner characterized by having a Carr""s fluidity index of 30 or more. The higher the fluidity index is, the more lightly fluid the toner can be. As a toner, however, if the toner has only a fluidity index of 30 or more, the toner may be agitated with difficulty, and also may be fed to the developing sleeve with difficulty. Hence, it is difficult to detect any accurate powder quantity of the toner. Also, some toners may come loose with difficulty when packed even in the case of toners having a high fluidity. Namely, when the toner is filled, the toner having been pressed and compacted at the bottom of a cartridge by the toner""s own weight, the toner may be agitated by means of an agitation member with difficulty and may be fed to the developing member with difficulty. Hence, the quantity of usable toner may lower for its filling fraction (or packing fraction), thus it is difficult to detect the quantity of toner actually used. Japanese Patent No. 2943035 also discloses a toner specified to have a floodability index of from 50 to 80. However, in this case, too, this value is low for the use of the residual detection system. Even if the toner within this range is used in the cartridge, the toner may be agitated with difficulty as stated above and also may be fed to the developing sleeve with difficulty. Thus, it is difficult to learn the quantity of toner accurately.
In order to change this fluidity of toner, it is attempted to change the physical properties of a resin as disclosed in Japanese Patent Application Laid-open No. 07-281478, to change fluidity using a wax as disclosed in Japanese Patent Application Laid-open No. 2000-284522, and to change the fluidity of toner by changing the fluidity index of a magnetic material as disclosed in Japanese Patent Application Laid-open No. 06-230604. However, where the physical properties of various materials for toners are changed in order to attain the intended fluidity indices of the toners as in these cases, the toners may conversely have characteristics unsuitable for the developing processes in the main body, so that any good developing performance can not be achieved in some cases.
Japanese Patent Application Laid-open No. 07-160044 also discloses a method in which a toner has a fluidity index of 40 or more and the fluidity index is changed by selecting the type of an external additive and the conditions for its external addition. However, those which are chiefly disclosed therein are the amount of the external additive and the time for treatment by external addition, and the toner, though having a high fluidity, does not have any sufficient floodability. Hence, it does not have any sufficient powder characteristics for its incorporation in the residual detection system.
An object of the present invention is to provide a toner and a process cartridge which make it possible to detect the quantity of toner remaining in a toner-holding section, in any environment and at any filling fraction in the process cartridge to inform users of the residual of toner and the number of printable sheets, and to afford superior developing performance.
Stated specifically, the present invention provides a process cartridge used in an image-forming apparatus which forms an image on a recording medium, wherein;
the process cartridge is detachably mountable to the main body of the image-forming apparatus;
the process cartridge has a photosensitive member, a toner-holding section which holds therein a toner for developing electrostatic latent images formed on the photosensitive member and is provided with a toner-carrying member which transports the toner to a developing zone, and a toner-residual detection means capable of detecting residual toner by a change in electrostatic capacity which is caused between electrodes provided inside the toner-holding section; and
the toner contains at least a binder resin and a colorant, has a weight-average particle diameter of from 6.5 xcexcm to 15.0 xcexcm, and has a Carr""s floodability index of more than 80.